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Sexing koi- Photo By nishikigoi-info.com

Sexing Koi Fish

Females, especially in season are far more rounded than male fish which tend to be slim at all times. The pectoral fins of male fish tend to be larger and more pointed than those of female fish, but this is by no means always the case.

During the breeding season, male fish can display a rough surface to the gill plates, again however, not always. To be sure, net the chosen fish and apply gentle pressure along the lower abdomen wall with your thumb and forefinger towards the vent. Male fish show signs of milt from the vent, whereas females in season will provide eggs! This operation should however be performed with great care so as not to injure the fish. 

I find the only sure way to sex fish is to watch the fish. The ones that lay eggs are female, the ones that chase are the males

Pairing




This is always initially a process of trial and error. Always pair like varieties if you are trying to produce a certain variety. For example, if you are trying to breed kohakus, use kohaku male and female fish. Crossing a kohaku and sanke/showa is acceptable, crossing a kohaku and a Yamabuki for instance will probably produce only ghost and black koi.

Remember that male genes tend to be dominant in any pairing.  Always select adult fish only to ensure successful spawning. Once you have found a pairing that gives some good fish – keep it. If you find a pairing that produces show winners, give me a ring I'll buy them!!


Preparation
Separate males and females at least one month before you intend to spawn the fish.  Provide a reasonably small pond – ideal 2 x 3 x 1 meter deep  Or use a spawning net in your main pond.  Don’t feed the parent fish for a few days before you expect the fish to spawn.

Prepare your growing on pond(s) by seeding them with chicken manure or (if you are worried about your koi catching salmonella!) use leaf mold to encourage the production of infusoria and daphnia which the koi fry will need in abundance from day one.

Spawning




Spawning usually takes place 1 – 3 days after introducing male(s) to the female(s). It can take place at any time of day or night, unfortunately, typically spawning seems to happen around two am (about the same time as most babies are born!).  Spawning can be triggered by temperature changes, change in water conditions, introducing new fish or barometric pressure changes (i.e. thunder.)

Water Conditions

Koi will spawn when the water temperature reaches around 18 Deg +. As always, you need to ensure prime water conditions with zero   ammonia or other pollutants present.  I have found that the addition of Refresh or similar clay products to the water can to get them going ! To achieve and maintain the necessary water temperatures early in the season (late May) it is a good idea to provide heated conditions so that you can achieve a spawning as early as possible to maximize the length of the growing season.

Spawning media

I recommend using purpose made spawning ropes. These are soft and easy to handle.  Don’t use blanket weed – it is too difficult to collect the eggs without damaging them. A good quantity of media is required to collect all the eggs and encourage spawning.





 

Handling Fry

Once the fry have hatched, after about 4-5 days, depending on temperature you will need to move them to the growing on ponds. Fry can be moved even when a few days old using plastic bags or fine mesh net. Handle with care however since they are easily damaged.


Culling

Now comes the tricky part. To cull fry successfully you must:

• know the parent stocks;  

• have extremely good eyesight; 

• have experience;  

• and there are a few basic principles that should be followed; 

• watch out for Tobi they will eat and feast on their smaller siblings;  

For example, Utsuris and Showas should produce black fry. Whites and reds develop. You should destroy any fry which are not black. With kohaku /Sanke fry will tend to be orange or orange and white. Any pure white or black should be culled.

If you are breeding patterned fish you should generally speaking destroy all plain colored fry.   I find that the fry need to be at least 6-8 weeks old before I can see what I am doing!  The Japanese breeders start culling generally at 4 weeks.

As the fish get larger, cull out any with deformities, missing fins, two heads etc.  Ideally you should cull several times in the season, but in practical terms I find that Herons and Kingfishers do more culling than I do!.  Culling is clearly important to reduce numbers to ensure that the fish that you want reach a reasonable size by the end of the season.


Feeding

The fry need an ample supply of live, natural food if they are to survive and grow quickly. Providing the proper growing on pond environment is the surest way to provide a good supply of daphnia and infusoria, on which the fry will develop. Whilst tempting. no dry or artificial food should be given to fry for at least six to eight weeks – it can damage the gills and is also likely to pollute the growing on pond. Any slight build up of ammonia or nitrite will kill fry very quickly indeed.

Growing 

Fry normally reach between 2 and 4 inches by mid October assuming spawning in early June. Factors which will affect growth rates are: - temperature, food supply, volume of fish and variety. If you don't cull, you may end up with a lot more babies, but they will be very much smaller than desired. Also of course, your food source will be depleted that much faster.

Unfortunately Runts and plain fish grow quickest !. Showa, Utsuri, Kohaku and Sanke seem to be slowest. Another reason why culling is so important.

The growing on environment is also important since baby koi don’t grow well in man made filtered ponds because of a lack of natural food and are vulnerable to pollutants in water especially nitrite.